USPTO Patents Application 10634351

Europaisches Patentamt
European Patent Office
Office europeen des brevets

© Publication number:

0 448 259 B1

EUROPEAN PATENT SPECIFICATION

© Date of publication of patent specification: 22.11.95 © Int. CI. 6 : C08L 23/06, //(C08L23/06,

_ 91:00)

© Application number: 91301938.6
© Date of filing: 08.03.91

© Process for the extrusion of low density polyethylene.

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© Priority: 09.03.90 US 490846

© Date of publication of application:
25.09.91 Bulletin 91/39

© Publication of the grant of the patent:
22.11.95 Bulletin 95/47

© Designated Contracting States:
BE FR GB IT SE

© References cited:
DE-A- 3 630 682
US A- 4 415 691

© Proprietor: UNION CARBIDE CHEMICALS AND
PLASTICS COMPANY, INC.
39 Old Ridgebury Road
Danbury

Connecticut 06817-0001 (US)

@ Inventor: Rifi, Mahmoud Rashad
28 Dawson Road
Kendall Park,
New Jersey 08824 (US)

© Representative: Allard, Susan Joyce et al
BOULT, WADE & TENNANT
27 Furnival Street
London EC4A 1PQ (GB)

Note: Within nine months from the publication of the mention of the grant of the European patent, any person
may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition
shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee
has been paid (Art. 99(1 ) European patent convention).

Rank Xerox (UK) Business Services

13. 10/3.09/3.3.3>

EP 0 448 259 B1

Description

This invention relates to a process for the extrusion of polyethylene, which has a density equal to or
less than about 0.915 gram per cubic centimetre {low density polyethylene).

The low modulus of commercial rubbers such as ethylene/propylene copolymers (EPM) and plasticized
polyvinyl chloride (PVC) make these rubbers very useful in such applications as hose and tubing. In
addition, PVC finds extensive use in film and other applications in which compliance with Food & Drug
Administration (FDA) requirements is necessary. Because of its higher modulus, polyethylene including low
density polyethylene has found limited utility in the aforementioned applications even though it has other
advantageous qualities such as toughness and chemical resistance.

DE-A-3 630 682 discloses an extrusion process comprising blending low density polyethylene with an
additive comprising corn oil, polybutene, stearate, petroleum resin and extruding the blend. The product
may be used as an improved food wrapping film.

An object of this invention, therefore, is to provide a process which will not only serf to extrude the
polyethylene into, for example, hose, tubing, and film but will reduce its modulus to a level at which it will
be competitive with its EPM and PVC counterparts.

Other objects and advantages will become hereinafter.

According to the present invention, there is provided an extrusion process comprising blending a
copolymer of ethylene and a minor amount of one or more alpha-olefins having at least 4 carbon atoms,
said copolymer having a density equal to or less than 0.915 gram per cubic centimetre; a molecular weight
in the range of 150.000 to 300,000; and a melt index in the range of from 0.05 to 1.5 gram per 10 minutes
as determined under ASTM D-1238, Condition E, with a liquid hydrocarbon oil having a viscosity of at least
2500 SUS (Saybolt Universal Seconds) at 37.8 "C in an amount of 5 to 20 parts by weight of oil per 100
parts by weight of copolymer; and extruding the blend.

The copolymer of ethylene and an alpha olefin having less than 4 carbon atoms is termed low density
polyethylene herein. The copolymer comprises a minor amount of one or more alpha-olefins having at least
4 carbon atoms, and preferably having 4 to 8 carbon atoms. The low density polyethylene can be prepared
by the process described in EP-A-No.O 120 501 published on October 3, 1984.

The low density polyethylene can be in the form of porous granules or pellets. The porous granules of
the low density polyethylene generally have a diameter in the range of about 25 micrometres to about 2500
micrometres. Regardless of its form, the low density polyethylene has a density equal to or less than about
0.915 gram per cubic centimetre, preferably in the range of 0.870 to 0.915 gram per cubic centimetre. If the
low density polyethylene is in pallet form, the blending step is carried out with the polyethylene in the
molten state.

The molecular weight of the low density polyethylene can be in the range of 150.000 to 300,000 and is
preferably in the range of 150.000 to 250,000. Thus, the melt index is preferably in the range of 0.1 to 1.5
grams per 10 minutes. Melt index is determined under ASTM D-1238. Condition E. It is measured at 190°C
and reported as grams per 10 minutes.

The portion of the copolymer attributed to the alpha-olefin comonomers can be in the range of 5 to 50
percent by weight based on the weight of the copolymer and is preferably in the range of 10 to 30 percent
by weight based on the weight of the copolymer. The balance of the copolymer is based on ethylene. The
preferred comonomers are 1-butene, 1-hexene, and 1-octene.

The liquid hydrocarbon oil is generally a petroleum derived processing oil commonly used in the
compounding and extruding of rubber compositions. The major oil type present in any of these oils can be
aromatic or aliphatic. Examples of these liquid hydrocarbon oils are paraffin oils, naphthenic oils, and
" mineral oils. Liquid polybutene can also be included among the examples. Mixtures of the various oils can
be used, if desired. The oils can have preferably a viscosity upto 3000 SUS at 100 ' F (37.8* C).

In the case of porous granular low density polyethylene, the oils are usually dry blended with the
polyethylene prior to extrusion (preblending). but the oil and resin can be blended in the extruder itself, if
desired. Preblending is preferable, however, since it shortens the mixing time and is a key factor' in
achieving uniform distribution of the oil in the resin. In the case of pelletized low density polyethylene, the
low density polyethylene is in the molten state when the blending is initiated. The amount of oil introduced
into the blend of is in the range of 5 to 20 parts by weight of oil per 100 parts by weight of low density
polyethylene. The low density polyethylene mixes readily with the oil without the use of heat except, as
noted, when it is in pelletized form. Mixers and extruders useful in carrying out the process of the invention
are conventional off-the-shelf equipment. A typical extruder is described in US patent 4.857,600. Mixers,
which can be used to blend the resin and the oil, are Banbury or other internal mixers, two roll mills, or
Baker Perkins or similar sigma blade mixers. As noted, extruders can also be used to mix the resin and the

EP 0 448 259 B1

w

75

oil.

Advantages of the blend are improved processability in the extruder, e.g., a fractional melt index will
d.splay the extrusion behavior of a 1 to 2 melt index resin; avoidance of bleeding when oil is used in
preferred amounts; extrusion can be conducted under less pressure and amperage without sacrificing
products rates; hose and tubing made from the combination of high molecular weight low density
polyethylene and oil. when compared to plasticized PVC, have a lower brittle point, a higher softening
temperature, and better chemical and environmental resistance; and, with respect to extruded film the oil
modified low density polyethylene displays improved puncture dart drop and clarity. The production of film
from the oil mod.f.ed low density polyethylene is particularly useful in the preparation of products which
must meet FDA requirements. Thus, a low density polyethylene with, for example, a 0.910 g/cc density
which meets FDA requirements, can be blended with an oil. which also meets FDA requirements The result
is a product which has the properties of a low density polyethylene having a lower density than 0 910 o/cc
and still meets the FDA requirements.

Polyethylenes, in general, display poor compression set and resiliency. Compression set which is
determined under ASTM-D-395-85, is defined as the amount (in percent) by which a standard test piece
fails to return to its original thickness after being subjected to a standard compression load for a fixed
period of time. The better the compression set, i.e., the lower the percent, the more resilient the polymer
One more advantage of the oil modified low density polyethylene is its improved compression set relative to
the unmodified low density polyethylene. The compression set is further improved by crosslinkinq the oil
20 modified low density polyethylene.

Crosslinking is accomplished by using conventional techniques. The oil modified low density polyethyl-
ene can be crosslinked by adding a crosslinking agent to the composition or by making the resin
hydrolyzable, which is accomplished by adding hydrolyzable groups, such as -Si(OR) 3 wherein R is a
hydrocarbyl radical, to the resin structure through copolymerization or grafting.

Suitable cross linking agents are organic peroxides such as dicumyl peroxide; 2.5-dimethyl-2 5-di(t-
butylperoxy)hexane; t-butyl cumyl peroxide; and 2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3. Dicumyl perox-
ide is preferred. 1 K

Hydrolyzable groups can be added, for example, by copolymerizing ethylene with an ethylenically
unsaturated compound having one or more -Si(OR) 3 groups such as vinyltrimethoxysilane, vinyltriethox-
ysilane, and gammamethacryloxypropyl-trimethoxysilane or by grafting these silane compounds to the resin
in the presence of the aforementioned organic peroxides. The hydrolyzable resins are then crosslinked by
moisture in the presence of a silanol condensation catalyst such as dibutyltin dilaurate. dibutyltin dlacetate
stannous acetate, lead naphthenane. and zinc caprylate. Dibutyltin dilaurate is preferred

Conventional additives can be added to the oil modified low density polyethylene during the preblen-
ding step and/or the extrusion step. The amount of additive is usually in the range of 0 01 to 60 percent by
weight based on the weight of the resin. Useful additives are antioxidants, ultraviolet absorbers antistatic
agents, pigments, dyes, fillers, slip agents, fire retardants. plasticizers. processing aids, lubricants stabiliz-
ers smoke »nh,b«tors, viscosity control agents, vulcanizing agents, crosslinking agents, crosslinking cata-
lysts, and crosslinking boosters. ~
40 The invention is illustrated by the following examples.

Examples 1 to 4

25

30

35

Porous granular low density polyethylene having a density of 0.910 gram per cubic centimeter and
45 prepared using the catalyst and process described in European Patent Application 0 120 501 referred to

^SUS^7 8 COm0n ° mer iS 1 " heXene " The 0H is 3 paraf,ln oil havin 9 a viscosity of

The low density polyethylene and the oil are mixed in a ribbon blender for 15 minutes. The mixture is
then pellet.zed. and the pellets are extruded in an extruder to provide a film having a thickness of 0 025mm
so (0.001 inch). The extruder operates at 60 revolutions per minute, the die gap (or die diameter) in the
extruder ,s 0.025mm (0.001 inch); and the BUR is 2:1. The BUR is the blow-up ratio. This is the ratio of die
diameter to bubble diameter. The bubble diameter is 2 X layflat/pi. The "layflat" refers to the width of the
flattened bubble.

It is found that the modulus ot the oil modified low density polyethylene is approximately the same as
55 otherwise equivalent commercial EPM's and PVC's.

EP 0 448 259 B1

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EP 0 448 259 B1

Claims

1. An extrusion process comprising:

(i) blending a copolymer of ethylene and a minor amount of one or more alpha-olefins having at
least 4 carbon atoms, said copolymer having a density equal to or less than 0.915 gram per cubic
centimetre; a molecular weight in the range of 150,000 to 300,000; and a melt index in the range of
from 0.05 to 1.5 grams per 10 minutes as determined under ASTM D-1238, Condition E. with a
liquid hydrocarbon oil having a viscosity of at least 2500 SUS (Saybolt Universal Seconds) at
37.8 'C in an amount of 5 to 20 parts by weight of oil per 100 parts by weight of copolymer; and

(ii) extruding the blend.

2. A process as claimed in claim 1 wherein the copolymer is in a porous granular form.

3. A process as claimed in claim 1 or claim 2 wherein the blending is conducted with the copolymer in
the molten state.

4. A process as claimed in any one of the preceding claims wherein the density of the copolymer is
above about 0.870 gram per cubic centimetre.

5. A process as claimed in any one of the preceding claims wherein the molecular weight is in the range
of from 150,000 to 250.000.

6. A process as claimed in any one of the preceding claims wherein the melt index of the copolymer is in
the range of from 0.1 to 1.5 grams per 10 minutes.

7. A process as claimed in any one of the preceding claims wherein the oil is a paraffin oil, a naphthenic
oil, a mineral oil, polybutene. or a mixture of two or more of such oils.

8. A process as claimed in any one of the preceding claims wherein the copolymer and the oil are
blended in an extruder.

9. A process as claimed in any one of the preceding claims wherein a cross linking agent is blended with
the copolymer or incorporated into the mixture of copolymer and oil during extrusion, and cross linking
of the copolymer is effected either during or after extrusion.

10. Process as claimed in any one of the preceding claims for producing an extruded product in the form
of a hose, tubing or film.

Patentanspriiche

1. Extrusionsverfahren, umfassend

(i) Vermischen eines Copolymers aus Ethylen und einer kleineren Menge eines Oder mehrerer q-
Olefine mit mindestens 4 Kohlenstoffatomen. wobei das Copolymer eine Dichte gleich Oder kleiner
als 0.915 g/cm 3 , ein Molekulargewicht im Bereich von 150 000 bis 300 000 und einen Schmelzindex
im Bereich von 0,05 bis 1,5 g pro 10 Minuten, bestimmt nach ASTM D-1238, Bedingung E besitzt,
mit einem flussigen Kohlenwasserstoffol mit einer Viskositat von mindestens 2500 SUS (Saybolt
Universal Seconds) bei 37,8 *C in einer Menge von 5 bis 20 Gew.-Teilen Ol pro 100 Gew.-Teile
Copolymer und

(ii) Extrudieren des Gemisches.

2. Verfahren nach Anspruch 1, wobei das Copolymer in Form eines porosen Granulats vorliegt.

3. Verfahren nach Anspruch 1 Oder Anspruch 2, wobei das Vermischen mit dem Copolymer in geschmol-
zenem Zustand durchgefuhrt wird.

4.

Verfahren nach einem der vorangehenden Anspruche. wobei die Dichte des Copolymers oberhalb etwa
0,870 g/cm 3 liegt.

EP 0 448 259 B1

5. Verfahren nach einem der vorangehenden Anspruche, wobei das Molekulargewicht im Bereich von 1 50
000 bis 250 000 liegt.

6. Verfahren nach einem der vorangehenden Anspruche, wobei der Schmelzindex des Copolymers im
Bereich von 0,1 bis 1,5 g je 10 Minuten liegt.

7. Verfahren nach einem der vorangehenden Anspruche, wobei das 6l ein Paraffindl, ein naphthenisches
Ol, ein Mineralol, Polybuten Oder ein Gemisch aus zwei Oder mehreren derartigen Olen ist.

8. Verfahren nach einem der vorangehenden Anspruche, wobei das Copolymer und das Ol in einem
Extruder vermischt werden.

9. Verfahren nach einem der vorangehenden Anspruche, wobei ein Vernetzungsmittel mit dem Copolymer
vermischt Oder in das Gemisch aus Copolymer und Ol wahrend der Extrusion eingebaut wird und das
Copolymer entweder wahrend Oder nach dem Extrudieren vernetzt wird.

10. Verfahren nach einem der vorangehenden Anspruche zur Herstellung eines extrudierten Produktes in
Form eines Schlauchs, Rohrs Oder einer Folie.

Revendications

1. Procede d'extrusion, comprenant les etapes consistant :

(i) a melanger un copolymere d'ethylene et d'une petite quantite d'une ou plusieurs alpha-olefines
ayant au moins 4 atomes de carbone, ledit copolymere ayant une masse volumique egale ou
inferieure a 0,915 g/cm 3 ; un poids moleculaire compris dans I'intervalle de 150 000 a 300 000 ; et
un indice de fluidite compris dans I'intervalle de 0,05 a 1.5 g pour 10 minutes, determine suivant la
condition E de la norme ASTM D-1238, avec une huile hydrocarbonee liquide ayant une viscosite
d'au moins 2500 SUS (Secondes Universelles Saybolt) a 37,8 ' C en une quantite de 5 a 20 parties
en poids d'huile pour 100 parties en poids de copolymere ; et

(ii) a extruder le melange.

2. Procede suivant la revendication 1, dans lequel le copolymere est sous forme granulaire poreuse.

3. Procede suivant la revendication 1 ou la revendication 2, dans lequel le melange est effectue avec le
copolymere a I'etat fondu.

4. Procede suivant Tune quelconque des revendications precedentes, dans lequel la masse volumique du
copolymere est superieure a environ 0,870 g/cm 3 .

5. Procede suivant Tune quelconque des revendications precedentes, dans lequel le poids moleculaire est
compris dans I'intervalle de 150 000 a 250 000.

6. Procede suivant I'une quelconque des revendications precedentes. dans lequel I'indice de fluidite du
copolymere est compris dans I'intervalle de 0,1 a 1,5 g pour dix minutes.

7. Procede suivant I'une quelconque des revendications precedentes. dans lequel I'huile est une huile
paraffinique, une huile naphtenique, une huile minerale, un polybutene ou un melange de 2 ou plus de
2 de ces huiles.

8. Procede suivant I'une quelconque des revendications precedentes, dans lequel le copolymere el I'huile
sont melanges dans une extrudeuse.

9. Procede suivant I'une quelconque des revendications precedentes, dans lequel un agent de reticulation
est melange au copolymere ou incorpore au melange de copolymere el d'huile au cours de I'extrusion,
et la reticulation du copolymere est effectuee pendant ou apres I'extrusion.

10. Procede suivant I'une quelconque des revendications precedentes, pour la formation d'un produit
extrude sous forme d'un tuyau souple. d'un tube ou d'un film.